![]() NPS photo / B. Clayton ![]() NPS photo / G.M. Spoto When you arrive at Grand Portage National Monument and get out of your vehicle, your eyes will likely be drawn up to piles of broken rocks with a gray-green cast. Above the piles are cliffs in which you may be able to see horizontal layering; at your feet you may notice the layers slightly tilt towards the lake. Nearly two billion years old, these rocks are known as the Rove Formation. As you walk into the Heritage Center, you will see the tallest fireplace in the county. The trim in the Heritage Center and the fireplaces and foundations of reconstructed buildings in the historic depot are all built from this stone. The North West Company also used it in the original depot completed in 1789. On each side of the parking lot are dark, nearly vertical stacked rocks which stick out as walls because they are much harder than the Rove rocks between and are much harder for water and ice to break apart. ![]() NPS photo / M. Plummer-Steen Rugged hills and boggy lowlands, shear rock cliffs, shallow incised bays and Lake Superior, all come together in the highlands of Grand Portage. This extraordinary and impressive landscape was created by the different weathering rates of two types of rocks produced during Precambrian time. For nearly one billion years, stream erosion and glacial scour have removed much more of the soft than the hard rock leaving a modern relief of more than 600 feet. ![]() NPS photo / B. Clayton |
Last updated: October 31, 2022